1. Technical Field
The disclosure generally relates to an electronic device for providing power to a load that has different resistance values in different operation modes, and more particularly, to a telephone switchboard coupled between a network and a telephone.
2. Description of Related Art
Generally, a telephone has three operation modes including an on-hook state, a dialing state and a dialog state. In the on-hook state, the telephone is on standby and no calling signals are input to the telephone. In the dialing state, a calling signal is input to the telephone and the telephone is ringing. In the dialog state, users are able to transmit voice information to each other via the telephone. However, in these operation modes, the telephone has different operation resistance values. For example, when the telephone is in the on-hook state or in the dialing state, the telephone has an operation resistance value far greater than the resistance value when the telephone is in the dialog state. Therefore, a telephone switchboard is required to have an ability to generate different operation voltages relative to different modes of the telephone.